Transmission and reception of intelligence



Dec. 28, 1937. s. G. FRANTZ ET AL 2,103,745

'TRANSMISSIZON AND RECEPTION OF INTELLIGENCE Filed April 23, 1935 3 Sheets-Sheet 1 AMY/HER 4 mar/m 5- 8+ 540/0 MA/VSM/Tfffi INVENTORS 5.6- FRANTZ B. S. M UTCHEN ATTORNEY Dec. 28, 1937. s. G. FRANTZ ET AL 2,103,745

TRANSMISSION AND RECEPTION OF INTELLIGENCE Filed April 25, 1955 a Sheets-Sheet 2 INVENTORS 5. C1- FRANTZ 5.5. M UTCHEN ATTORNEY i I v I I POWER [fil/MHW WWI/Mm? [CM/[0L 53 74 I I 6a ,6 7/ :1 if

Patented Dec. 28, 1937 UNITED STATES PATENT OFFICE raANsMIssIoN AND RECEPTION oF" IN- TELLIGENCE Application April 23, 1935, Serial No. 17,775

6 Claims.

This invention relates generally to the transmission and reception of intelligence and is specifically directed towards improving the quality of the received intelligence. I

The present application isa continuation in part of co-pending application Serial Number F196,595 filed November 19th, 1930, entitled Trans mission and reception of intelligence now U. S. Patent No. 2,006,989 issued July 2, 1935.

More specifically, the present invention relates to systems and methods for maintaining the relations between the various increments of the intelligence issuing from an electrical energy. translating device at a receiving point substantially proportional to the relations between the various corresponding increments of the original intelligence.

An object of the invention is to provide a novel and eflicient method of transmission and reception of signals.

Another object of the present invention is the achieving of clear fidelity of reproduction at the receiving end of radio signals and in particular music, by partial or total compression of the intensity range, or range of modulation at the transmitting end and corresponding expansion of the intensity range at the receiving end.

In the proposed system the degree or percentage of modulation applied to the carrier wave at the transmitting end instead of being made directly proportional to the intensity of the signal in the microphone circuit is made to suffer a smaller percentage variation than the latter. This may be called range compression or sub-proportional modulation. Thus, in this system a weak signal will be more amplified before it is used for modulation than will a strong signal. A feature of our invention is then that the intensity range or the ratio between maximum and minimum percentage of modulation of the transmitted radio signal is less than the intensity range of the original signal. The extent or degree of this compression of intensity range may in practice result in about the same ratio of maximum to minimum percentage of modulation as is at present obtained by manual control at broadcasting stations; or, the compression may be carried much further even to the limit at which there is a total obliteration of intensity range and the signal is transmitted at constant percentage modulation. In general, in the present system the intensity range will be compressed but not obliterated.

At the receiving end of the present system means are provided to re-expand the intensity range to that existing in the original signal. These means at the receiver must be so arranged as to work in correspondence with the compression effected at the transmission station.

At this point we desire to emphasize the fact that one of the benefits that will'be derived from the use of our system will be the lessening of the effect of atmospheric disturbances upon the receiver.

The measure of the effect of atmospheric disturbances or other interference on the quality of reception is the ratio of interference intensity to signal intensity, and this effect will therefore be most pronounced when the signal intensity is low. With the present system, during weak original signals, the transmitted signal intensity will always be greater than it would be were there no compression of intensity range before transmission, and therefore the effect of interference is minimized. In other words, when weak signals are being transmitted the energy will be more amplified before it is used for modulation with the result that ordinary atmospheric disturbances will not obscure the signal.

v This invention relates to and comprises the above described compression and expansion of intensity range, and means for accomplishing the compression and expansion. I

In the subject matter hereinafter described there areproposed for this purpose three ways of informing the receiving apparatus as to what amount of expansion is necessary. The three cases may be classified as follows;

1. Separate wire or radio channel.

2. Variation of carrier frequency.

3. The use of the residual variation of modulation percentage itself as the signal which communicates to the receiving apparatus how much the signal should be amplified;

The simplest case of the latter would be logarithmic sub-proportional range compressionat the transmitter with corresponding logarithmic super-proportional range expansion at the receiver. Expressed mathematically we have:-

i I2: k I 3 M 2 z i where I1=original intensity 1 l I I2=transmitted intensity'of modulation Is=receiver output intensity I01 and 702 are constants and (1:2. constant 1.

In using the system described in the third subdivision it is obvious, of course, that the intensity range must not be completely obliterated.

An object of the present invention is to provide a specialiy constructed bridge arrangement for effecting the desired compression at the transmitter and expansion at the receiver.

Another object of the invention is the provision of a plurality of said specially constructed resistance bridges arranged in cascade.

Another object of the present invention is to provide means for performing the desired compression and expansion by varying the carrier frequency.

Still another object of the present invention is to provide a separate channel for the transmission from transmitter to receiver of the information necessary for the receiver to adjust itself for proper amplification.

Still other objects of the invention will be apparent from the following description of typical circuits according to our invention illustrated in the accompanying drawings, in which Figure 1 illustrates a transmitter arrangement of one form of our invention utilizing a so-called temperature bridge;

Figure 2 illustrates diagrammatically a method by which two or more temperature bridges may be cascaded; V

Figure 3 illustrates diagrammatically a receiver in accordance with our invention employing a temperature bridge arrangement for receiving and appropriately expanding signals transmitted from a system such as shown in Figure 1;

Figure 4 illustrates diagrammatically an alternative method of range compression in a transmitter circuit;

Figure 5 illustrates a receiver adapted to be used in conjunction with a transmission system such as shown in Figure 4;

Figure 6 illustrates diagrammatically a range compression transmission circuit utilizing the variable frequency carrier method;

Figure 7 illustrates diagrammatically a receiver for receiving signals and appropriately amplifying them for a transmission system. such as that shown in Figure 6;

Figure 8 illustrates diagrammatically a transmitter adapted to perform the desired compression of the signal intensity and utilizing a separate channel for the transmission of the information to the receiver; and,

Figure 9 is an appropriate receiver for the system disclosed by Figure 8. 7

Referring to Figure 1 a microphone circuit is shown composed of microphone 5, transformer I and the usual source of current 6. An amplifier for the current generated in the microphone circuit is shown generally at 8 coupled to the microphone circuit by means of the transformer 'l. The output of the amplifier 8 is connected to a temperature bridge 9 by means of conductors I3 and i2 connected to diagonal points hi and I5 respectivelyof the bridge 9. The other two diagonal points of the bridge 9, namely, 55 and I! are connected by conductors M and in respectively, to a modulator and radio frequency energy source circuit of any well known design. Referring more particularly to the temperature bridge l, 2, 3 and i compose the four elements thereof. Elements i and are'of the same material and elements 2 and 3 are of some other material having a different temperature coefficient of resistance than said first material. The wires it will be evident are appreciably heated by the passage of the currents due to the signal voltage applied from the amplifier output. With maximum signal voltage the bridge is hottest and the resistances are so proportioned that under this condition the bridge is almost balanced; that is, the ratio of bridge output voltage to bridge input voltage is a minimum. With very low input voltage the bridge is comparatively cold and has a maximum of unbalance and hence the ratio of output to input voltage is'a maximum. Thus the bridge acts as a non-proportional attenuator, attenuating strong signals more than weak ones. While we do not intend to limit ourselves to any particular construction of the bridge one way on which the bridge could be constructed Would be of small Wires about the size of flash-light bulb filaments. Either I and i or 2 and 3 may be resistances so designed as to heat but little.

Broadly, the term temperature bridge as used herein includes any network with input and output connections in which the ratio of output to input voltage varies according to the input voltage as a result of change of resistance of any of the elements of the network due to heating by the current passing through it.

Attention is now directed to Figure 2. In said figure conductors i2 and i3 correspond to the conductors l2 and i3 leading from the output of the amplifier 8 ofFigure 1. Conductors l2 and I3 are connected to diagonally opposite points 2i and 25 respectively of the temperature bridge I8. The other two diagonally opposite points 22 and 23 of the bridge I8 are connected by conductors 24 and 25 respectively to two diagonally opposite points 2? and 26 respectively of a second temperature bridge device iii. The other two points of said last named bridge, namely, 23 and 29 may be connected either to another similar. bridge arrangement or to the modulator andradio fre quency energy source as shown by Figure 1 through the medium ofconductors i6 and II. It will thus be evident that in the arrangement shown any number of temperature bridges may be connected in cascade for obtaining any results desired.

Attention is now directed to Figure 3 which shows a receiver adaptedto properly expand the signals which were compressed by the transmitter shown in Figure 1. In Figure 3, 33 represents generally a stage of audio frequency amplification in an ordinary radio receiver. Coupled to the output of said stage by means of transformer 3i is a temperature bridge 32 in accordance with our invention. It will be noted that the secondary of the transformer M is connected by conductors 33 and 45 to two diagonally opposite points of said bridge 32. The other two diagonally opposite points of the bridge are connected by means of conductors 35 and 36 to the input of an amplifier generally shown at 3!. The output of this amplifier 37 is connected by means of conductors 39 and 38 to a receiving instrument shown generally as a telephone receiver 43. The bridge 32 is made up of elements i, 2, 3 and 4 which operate in a. somewhat similar manner to that described above in connection with Figure 1 except that in the case of the receiver, the bridge will be in approximate balance for minimum signal, so that in Figure 3 the greater the applied electrornotive force 6 across the secondary or" the transformer 3i the greater will be the resistance of elements I and 3 compared to the resistance of elements '2 and 3. 'Ihis condition causes an increased unbalance of the bridge and an increased output current. It is to be distinctly understood that 7 while we have shown only one bridge arrangement in the receiver shown in Figure 3 two or more such bridge arrangements may be arranged in cascade as shown in Figure 2.

Attention is now directed to Figured which shows an alternative method of range compression and Figure 5 which shows a receiver for receiving signals sent out from an arrangement shown by Figure 4. In Figure 4 a microphone circuit comprising microphone 5, transformer 4i and source of current 5 is shown coupled to a modulator tube 42 through the medium of said transformer 4!. The input circuit of the modulator tube 82 is also adapted to receive an alternating electro-motive force at some supersonic frequency from an oscillator. For this purpose we have shown the'supersonic oscillator diagrammatically as 53 feeding the alternating electromotive force to the input of the modulator tube through the: transformer M the secondary of which is placed in the grid cathode circuit of the modulator tube 42. It will be seen that with the arrangement so far described the output of the modulating tube 42 is then in the form of a supersonic carrier wave modulated by the voice frequency. An auxiliary winding on the microphone transformer ll is connected to the grid of a biased rectifier tube 45 which tube as will be seen from the drawings has its input circuit coupled to the microphone circuit. A biasing means 45 is shown connected in the grid-cathode circuit of tube 45. It will be seen that with the connection as shown, that is, because of the bias the direct component of the plate current of this rectifier tube &5 varies with changes in intensity of the voice signal or rather of the microphone circuit energy. This variation in plate current is used to change the bias on the grid of an amplifier tube 5! which tube has its input circuit coupled to the output of tube 42'. The arrangement of the circuit including the tube :i'l'is such that the variation in the plate current of tube 45 changes the bias on the grid of tube 47 in such a way that an increase of voice signal input causes a decrease in the gain in the amplifier tube t! by biasing its grid more negatively. For this purpose there: is provided in the plate circuit of tube 45 a resistance 4 8 in series with the plate current supply 511. The input circuit of the tube 41 includes a condenser 45! and means comprising a conductor 52 and a conductor 5! connected to a variable contact for placing any desired portion of the resistance 18 across the condenser 59. The output of the amplifier tube 4'! is fed to a detector 54 through a coupling transformer 53. The detector tube serves the purpose of separating the audio component of the energy fed therein. This audio component is then fed into a conventional radio transmitter 55 through the medium. of coupling transformer 55. The purpose of supplying the local supersonic frequency from the oscillator and later removing this frequency is to permit distortionless volume control in the amplifier tube ii.

The range expander for the system shown in Figure 4 will now be taken up. It should be understood that the operation of the range expansion system at the receiver is essentially the inverse of that of the range compressor at the transmitter. Referring to Figure 5 there is shown a usual antenna circuit 51 coupled to a radio frequency amplifier tube 59 through the medium of a tuned circuit 58. The output of the tube 59 is coupled to the input of a second radio frequency amplifier 6| through' a transformer 60. This second radio frequency tube has connected in its grid cathode circuit a condenser Hi shunted by a source of current 73 and a resistance H. The connection between the source of current i3 and the resistance ii is made variable for a purpose which will be later described. The output of tube ti is connected to the input of a detector tube 53 through a coupling transformer 52 and the output of the detector tube is coup-led to any desired type of audio frequency amplifier shown generally as through an audio transformer 6 An auxiliary detector tube 6'! is provided which is shown also coupled to the antenna through the medium of tuned circuit 55. This tuned circuit is tuned synchronously with the main tuning of the receiver in any desired manner now in use, such as any of the well known uni-control systems. The audio output of tube 5'! is fed into a biased rectifier tube 69 through the medium of transformer 63. Due to the biasing on the tube 69 the plate current thereof increases with an increase in signal intensity. It should be noted that part of the plate circuit of tube 59 is made up of the resistance H in series with. 4,

gain in this stage and increasing the output ini tensity. It should here be noted that in the range compressor shown in Figure 4 there is shown a large capacity ll connected across the plate and filament of the tube 45 and a choke coil 18 in series with the plate resistance 53. The object of this capacity and inductance is to prevent rapid variations in the bias of the amplifier tube 47 so rapid as to constitute an audio frequency disturbance. In Figure 5, condenser 55 has a similar function.

Attention is now directed to Figure 6 in which we have shown an arrangement in which for purposes of communicating to the receiver the amount that the receiver should amplify there is employed a system which makes use of socalled carrier wave frequency variation. In said figure the usual microphone circuit comprising microphone 5 and source 5 is shown coupled by means of transformer til to the input of a range compressor shown generally as 5i. This range compressor may be of any suitable design, such as, any one of the range compressors shown in' this application. The output of the range compressor 6| is coupled to a modulator by means of a coupling transformer 52. The modulator may be of any desired form and is shown generally at 63. The voice input transformer 6!! has a third winding 54 which is connected to a grid of a biased rectifying tube 65. This tube is arranged so that variations in the intensity of the voice current are manifested as a change in the magnitude of the direct component of the plate current of this biased rectifier tube. In the plate circuit of tube 65 there is the winding of a solenoid 55. The armature 6i of said sole-- noid is arranged to operate on a plate 53 of a small condenser 55 which is connected in parallel with the main tuning condenser iii of the main carrier frequency master oscillator ll. This masteroscillator feeds into the modulator cirfilament of the tube 05.

arrangement is to prevent the 1000 cycle note cuit 63 through a coupling I2 and the modulated carrier wave is relayed into the radio frequency power amplifier shown generally at 14 through the coupling transformer I2. From the power amplifier 7 5 the modulated carrier wave properly amplified is radiated as is usual through an.

antenna It. It is evident from what has preceded that the frequency of the carrier wave generated at Ii is varied or wobbled in accordance with the intensity of the voice input at 5 by means of the arrangement comprising the solenoid 00, armature 0i and variable condenser 69. The receiver for the system shown in Figure 6 will now be described.

Reference will now be had to Figure '7 in which l5 represents a receiving antenna. Coupled to the antenna '?5 through coupling transformer 16 is the usual radio frequency amplifier shown generally at T5. The amplifier output is directed to a variable gain tube '58 through a transformer '59. The output of the variable gain tube 18 goes to a detector tube 823 and from thence to an audio amplifier in customary manner. Coupled the antenna is a pickup coil 8! which forms part of the input circuit of a space discharge device 82. he grid circuit of this tube is so arranged that it receives an electroinotive force from a local oscillator shown generally at 83 through a transformer 8 3-. This oscillator must be tuned with the main receiver and may be tuned simultaneously therewith or separately if desired. The oscillator is not tuned to the exact carrier frequency but to a frequency difierent from the nominal carrier frequency by some standard amount, say, 1000 cycles. At the transmitting end the arrangement is such (see Figure 6) that with no voice input the radiated frequency is the nominal carrier frequency, therefore, at the receiving end (see Figure 7) with no voice input there will be a heat frequency in the output of tube 02 of 1000 cycles. Tube 82 is biased so as to give this beat product. The output of tube 32 is coupled to a tuned circuit 34' which is permanently tuned to respond to a frequency of 1000 cycles. The tuned circuit it will be noted forms a portion of the input circuit of tube 85 which tube is biased so as to rectify. A variation in the original signal intensity at the transmitting end, say an increase of signal intensity, will produce an increasing'variation of carrier frequency from normal carrier frequency. The beat note in the output of tube 32 will thus change from 1000 cycles to some less amount. This results in a decrease in the response of tuned circuit 84 and a decrease therefore in the input of tube 85. Tube is biased by means of source 86 so that a decrease in the grid input results in a decrease in the direct component of the plate current.

' This decreases the voltage drop across a resistance 81 in the plate circuit of tube 85 which resistance is connected in the grid return of the radio frequency amplifier tube I8 in the main receiver. Thus, an increase in original signal intensity decreases the plate current of tube 85, thus, decreasing the negative bias of the radio frequency amplifier tube '58 and increasing the gain of the main signal in this tube. In this way the amplification is greatest for greatest original signal intensity.

In the plate circuit of tube 85 there is shown a choke coil 00 and a large condenser 89', the condenser being connected across the plate and The purpose of this being applied to the grid of the that is, in the compressors and expanders. If this delay is found large enough to produce objectionable results its effect may be counteracted in the systems using separate channel or frequency variation by interposing in the circuit at the transmitting station an electric delay circuit of any well known kind, of time constant long enough to compensate for the objectionable delay. This electric delay circuit must be placed in the main voice circuit after the branch takeoff has been made for operating the frequency variation or the separate channel signal.

-Reference is now made to Figure 8 in which we have shown our invention embodying the use of a separate channel for the transmission from the transmitter to the receiver of the information necessary for the receiver to adjust itself to an appropriate degree of amplification. In Figure 8 a microphone circuit including microphone 5, source of current 6 and transformer ltd is shown connected through the transformer I00 to a range compressor IOI which may be of any suitable design such as any of those shown herein. The output of the range compressor is shown as leading to a radio or Wire channel No. 1. The microphone transformer Iiiil also has a third winding I02 connected to the input of a biased rectifier tube I03 which is so connected that its plate current varies with changes in the signal intensity. A large capacity I05 is shunted across the plate and filament of tube I 03 and a choke coil I05 is placed in series with the plate of tube I03 in order to prevent rapid changes in the direct component of the plate current. This direct component passes through a resistance I06 which is shown associated with the plate circuit of the tube I03. The voltage drop across this resistance is used to change the bias of an amplifier I01. The amplifier tube has impressed upon its grid 2. low frequency electroinotive force from a suitable oscillator !08. This frequency may be of the order of 100 to 1000 cycles. The output of the amplifier tube I0? is put on to the radio or wire channel which is to be used for purposes of range expansion control. In the drawings this is referred to as channel No. 2.

Attention is now directed to Figure 9 which shows a receiver which can be used for receiving signals in accordance with the system disclosed in Figure 8. In Figure 9 the main signal comes in on radio or wire channel No. l, is passed through an amplifier H0 and is impressed upon the grid of tube III. The output of this tube is connected to a usual detector H2 from there to the customary amplifier l 53 and to the telephone circuit H4. The intensity signal comes in over radio or wire channel No. 2, is directed through an amplifier H5 and is then impressed upon the grid of tube I I6 which is a biased rectifying tube so arranged that the direct component of its plate current is a function of the intensity of the signal impressed upon its grid. A condenser II! and choke coil H8 are provided and shown as connected to the plate circuit of tube I I6 for the same purpose as previously described in connection with Figure 8, reference being had to condenser IM and coil I05. Variations in the direct component of the plate current are manifested as a variation in the voltage drop across a resistance H9 in series with the plate circuit of tube I Hi. This drop is used to vary the grid bias of tube III in such a way that an increased gain will result in this tube from a decreased intensity of signal on channel No. 21, this signal on channel No. 2 having been arranged in the transmitting end to increase with decrease in original signal intensity.

It is to be understood that in a system such as shown in Fig. 8 the output of. the range compressor Ill! and the output of the amplifier I01 may be used to individually modulate a single carrier, in which case the compressed signals and the controlling signals are derived at the receiver from the same carrier.

.We claim:

1. The steps in a method of communicating signals of variable intensity which comprise, compressing the intensity range of the original signals, transmitting the compressed intensity range signals by modulating a carrier wave by the compressed intensity range signals, generating an auxiliary frequency which is low relative to the frequency of the compressed signals, modulating a carrier wave by said auxiliary frequency and controlling the degree of modulation thereof by the average intensity of the original uncompressed signals.

2. The steps in a method of communicating signals of variable intensity which comprise, compressing the intensity range of the original signals, transmitting the compressed intensity range signals by modulating a carrier wave by the compressed intensity range signals, generating an auxiliary wave having a frequency which is outside the range of the more important audible frequencies, modulating a carrier Wave by said auxiliary wave and controlling the degree of modulation thereof by the average intensity of the original uncompressed signals.

3. In a signalling system for communicating signals of variable intensity, means for compressing the intensity range of the signals, means for generating a carrier wave, means for modulating the carrier wave by the compressed intensity range signals, means for generating an auxiliary wave the frequency of which is outside wave and means for amplifying the derived compressed intensity range signals in accordance with the magnitude of the derived auxiliary wave.

5. In a signalling system for communicating signals of variable intensity between two points, means for compressing the intensity range of the original signals, means for generating a carrier wave, means for modulating the carrier wave by the compressed intensity range signals, means for generating an auxiliary wave having a fre quency which is low relative to the frequencies of the signals, means for modulating a carrier wave by said auxiliary wave, means for controlling the degree of modulation thereof by the average intensity of the original uncompressed signals, means for transmitting the energy resulting from said ,two modulations, means for receiving the transmitted energy, means for deriving from the received energy the low frequency modulations and the compressed intensity range signals and means for amplifying the derived compressed intensity range signals in accordance with the magnitude of the derived low frequency modulation.

6. The steps in a method of communicating signals of variable intensity, which comprise compressing the intensityrange of. the original signals, modulating a carrier wave by the compressed signals, generating an auxiliary frequency, modulating a carrier wave by the auxiliary frequency, and controlling the degree of said last named modulation in accordance with the average intensity of the original uncompressed signals.

' SAMUELG. FRANTZ.

BRUNSON S. MCCUTCHEN. 

